Electrical connectors for coaxial cables



ach 24, 1970 w. G. ALBERT 3,502,788

ELECTRICAL CONNECTCRS FOR COAXIAL CABLES Filed July 11, 1968 L! FIG.

TELEPHONE CENTRAL OFF/CE OPERA TING C/RCUI T5 FIG? /g 60 IN l/E N TOR By W. GILBERT A T TORNE V United States Patent 3,502,788 ELECTRICAL CONNECTORS FOR COAXIAL CABLES William G. Albert, Tewksbury, Mass., assignor to Bell Telephone Laboratories, Incorporated, Murray Hill, N.J., a corporation of New Jersey Filed July 11, 1968, Ser. No. 744,194 Int. Cl. H02g /08 US. Cl. 17488 11 Claims ABSTRACT OF THE DISCLOSURE In a connector, a rigid cylindrical shell is secured to a coaxial cables outer conductor, A conductive tube, centrally supported in the shell, receives the cables center conductor, Radial openings in the shell and tube furnish access for soldering the center conductor in the tube. A removable shield embraces the shell.

The connector serves as a cable termination when a resistor is soldered between the tube and shell. It may be converted to a splice by removing the resistance and soldering a second coaxial cables conductors to the tube and shell.

BACKGROUND OF THE INVENTION This invention relates to electrical connectors, particularly for forming connections from lengths of coaxial cable to other lengths or to other electrical components.

In telephone transmission terminals, such as central offices, coaxial cables often carry incoming and outgoing signals to and from compact filter, amplifying or other systems. These systems are often furnished with spare or emergency capacity in the form of unused circuits. To keep these spare circuits available without the need to enter and disturb the compact systems, the circuits are furnished short lengths of coaxial known as pigtails to which coaxial cables can be connected. At the same time, to prevent signal reflections at the end of this short length of coaxial cable from degrading the performance of the entire system, terminating impedances are connected to each spare circuit. Removal of such terminating impedances often involve disturbing the spare circuits. Moreover, craftsmen, after connecting the pigtails to cables, mistakenly fail to remove these impedances. This tends to degrade the operating performance. However, regulators which serve to make up for such errors conceal this degradation until enough such errors have accumulated to overcome the effect of the regulator. Then the entire system is suddenly degraded.

Temporary terminating impedances using pressure contacts have been proposed. This proposal was based on the assumption that such easily removable terminations, which do not require soldering and unsoldering, would be more likely to be removed. However, such terminations can be removed and accidently not replaced as they should be when the system is serviced. This results in distortions from reflections at the ends of the pigtails.

The invention According to the invention, these deficiencies are overcome by arranging to terminate the circuit at the endsof the pigtails. This is done by securing to the outer conductor at the end of the pigtail a rigid tubular shell with a radial aperture that exposes a coaxially mounted center tube which in turn axially receives the pigtails center conductor from one end and another conductor from the other end, and by opening the center tube so that solder may be applied to the center conductor and other conductor through the radial aperture. Sleeve-like shielding ice means surrounding the shell and secured thereto electromagnetically close it.

According to another feature of the invention, the resulting connector is used as a termination by making the other conductor part of a terminating impedance that fits into the shell and whose other end is soldered to the shell. The connector may serve as a splice by making the other conductor the center conductor of a coaxial cable and securing its outer conductor to the other end of the shell.

According to still another feature of the invention, the shell has a diameter along its center larger than along its ends and large enough so that together with the diameter of the central tube and the shielding means the characteristic impedance of the connector corresponds to the characteristic impedance of the pigtail coaxial cable to which it is connected.

According to yet another feature of the invention, the diameters at the ends of the shell are substantially the same as the diameters of the outer conductors on the coaxial cables from which the shell extends. Preferably the outer conductor of the cable or cables connected to the shell surround the small end of the shell and are crimped thereon by a soft metal ferrule.

By virtue of these features a pigtail of coaxial cable may be terminated with a terminating resistor soldered to the center tube as well as the shell and easily connected to another coaxial cable without the terminating resistance. To connect a coaxial cable to the terminated pigtail a craftsman removes the sleeve-like shielding means so as to expose the cut-away portion of the center tube through the aperture in the shell. He then unsolders the terminating impedance and replaces it with the center conductor of the cable to be connected. This center conductor is then soldered in the center tube and the outer conductor crimped about the end of the shell. The sleevelike shielding means are then moved axially over the shell and secured in position.

These and other features of the invention are pointed out in the claims. Other advantages and objects of the invention will become known from the following detailed description when read in light of the accompanying drawmgs.

Brief description of the drawings FIG. 1 is a schematic representation of a telephone central office with connections embodying features of the invention;

FIG. 2 is a partly sectional elevation showing the details of a terminating connection at the end of the pigtails of FIG. 1 and embodying features of the invention;

FIG. 3 is a partly sectional exploded plan view of the connection in FIG. 2; and

FIG. 4 is a sectional plan view showing the details of the splice in FIG. 1.

Description of preferred embodiment In FIG. 1 short cable lengths 10 emerge from the inputs and outputs of operating circuits 12 of a telephone central ofiice 14. Some of these circuits are utilized normally and others constitute the spare capacity for emergency use and growth. The circuits are generally compact and not easily accessible for connecting or disconnecting cables. Splice connections 16 connect those of the lengths 10 which issue from the operating circuits being utilized, to coaxial cables 18. Terminating connections 20 terminate those of the lengths 10, which emerge from the unused spare circuits and thus are not connected to coaxial cables 18, in suitable impedances. The terminating connections 20 each include an impedance corresponding to the characteristic impedance of the coaxial cables 18 so that reflections from the connections 20 do not degrade the operation of the circuits 12.

The lengths which are not connected to cables 18 form so-called pigtails 21. By extending out of the often inaccessible operating circuits 12 the pigtails 21 furnish access to the spare capacity in the circuits 12. Thus in the event of breakdown in any of the operating circuits 12 being utilized or in any of the coaxial cables 18, new coaxial cables may be spliced to the terminated pigtails 21.

FIGS. 2 and 3 illustrate the details of a connection 20. Here, a ferrule 22 that has been inwardly crimped squeezes the outer conductor 24 of the terminated cable 10 against a rigid cylindrical flange 26 that extends integrally and axially outward from a cylindrical shell 28. The shell 28 then forms a rigid electrical extension of the outer conductor 24. Dielectric disc spacers 30 mounted in the shells cylindrical body 32 coaxially support a central conducting tube 34. The latter receives the center conductor 36 of the cable length 10. A cylindrical dielectric spacer material 38, which spaces the center conductor 36 from the outer conductor 24, projects into the flange 26 close to the spacer 30. The center conductor 36 projects into the tube 34 far enough to emerge at a solder well 39 that has been notched in the tube. A solder bead 40 sweated into the tube at the well 39 secures the center conductor 36 to the tube 34.

A second solder head 41 sweated into a second solder well 42 secures the tube 34 to a conductive lead 44 emerging from a terminating resistor 46 and extending coaxially through the tube 34. The other lead 48 from the terminating resistor 46 is soldered by a solder head 50 to a second cylindrical flange 52 projecting coaxially from the body portion 32 of the shell 28.

Two radial access openings 54 in the body 32 expose the wells 39 and 42 to a craftsman so that the solder beads 40 and 41 may be applied for securing the lead 44 and the center conductor 36 in the tube 34. A cylindrical conductive shield 56 covers these openings 54 to maintain the operating integrity of the connection and prevent electromagnetic leakage. A suitable threaded bolt secures the shield 56 to the shell 28. A shrunken plastic sleeve 60 made of heat shrinkable plastic tubing fits snugly about the plastic outer jacket 62 of the cable length 10 and the ferrule 22.

The terminating connection 20 is formed by cutting back the spacer material 38 and the outer conductor 24 from the center conductor 36 and further cutting back the outer jacket 62. A craftsman then slides the initiallyexpanded heat shrinkable sleeve 60 and the ferrule 22 about the cable length 10. He then spreads the outer conductor so that the flange 26 fits between the outer conductor 24 and the spacer material 38 while the center conductor 36 passes into the tube 34 as far as the well 39. He then crimps the ferrule 22 about the outer conductor 24 and against the flange 26. After cutting the lead 44 on the terminating resistor 46 to size, he pushes the lead 44 into the tube 34 as far as it will go so that it emerges at the well 42 near the center conductor 36. He then solders the lead 48 onto the conductive flange 52 and sweats solder beads 40 and 41 into the tube 34 to connect it electrically and mechanically to the center conductor 36 and the lead 44. Preferably he provides an adequate supply of solder to flow and fill the tube 34. He can inspect the beads 40 and 41 as necessary. He completes the joint by sliding the shield 56 about the shell 28 and securing it with the bolt 58.

The diameter of the body 32 of the shell 28 is such that together with the shield 56 and the tube 34 it approximates the characteristic impedance of the cable in length 10 and the impedance of the resistor 46.

The shell 28, spacers 30, tube 34, shield 56 and bolt 58 form a connector C which is common to both the connections 16 and 20. 1

The splice connection 16 illustrated in detail in FIG. 4 corresponds substantially to the terminating connection 20 of FIG. 2 and is converted therefrom. However, here instead of the terminating resistor 46, the cable 18 is se- The connection 16 is converted from the connection 20 when it becomes necessary to cut in an unused central office circuit and therefore connect a cable 18 to the length 10 that emerges from the circuit being cut in. A craftsman connects the cable 18 by removing the bolt 58 and sliding the shield 56 over the cable length 10. He then unsolders the leads 44 and 48 of the resistor 46. Then, after cutting the end of the coaxial cable 18 to correspond with that shown in FIGS. 2 and 3 for the cable length 10 he pushes the center conductor '66 into the tube 34 until it emerges in the well 42 and the spacer material 68 abuts or nearly abuts against one of the spacers 30. At the same time he forces the flange 52 between the outer conductor 70 of the cable 18. He then crimps a ferrule 72 which he has earlier placed about the jacket 74 onto the outer conductor 70. After that he can easily solder the conductor 66 in the well 42. Before sliding the shield 56 back over the shell 28 and securing it with the bolt 58, he heat shrinks a tube 76 that he has p eviously placed over the outer jacket 74 of the cable 18, about the crimped ferrule 72 and a portion of the outer jacket 76. In this manner he obtains an inspectable splice connection.

The splice connection 16 as well as the terminating connection 20 maintains the coaxial relationship existing in the cable lengths 10 as well as the cables 18. Moreover, by adjusting the diameter of the shell 28 to conform to that of the tube 34 so as to furnish a characteristic imedance comparable to that of the length 10 and cables 18 the amount of reflection is minimized. That the center conductors 36 and 66 and the lead 44 are soldered in the respective connections 16 and 20 eliminates the noise that is likely to be imposed upon the microvolt level signals being passed by these conductors when pressure contacts hitherto used, age over their twenty to thirty year lifetimes. The resulting structure is easily convertible from a cable terminating connection to a cable splice connection. The time necessary for such conversion is small.

While embodiments of the invention have been described in detail, it will be obvious to those skilled in the art that the invention may be embodied otherwise without departing from its spirit and scope.

What is claimed is:

1. A cable connection comprising coaxial cable means having outer conductor means and center conductor means, rigid conductive tubular shell means connected coaxially to said outer conductor means, insulating spacer means mounted in said shell means and having centering means for holding said center conductor means coaxially in said shell means, said shell means having a radial opening for exposing the center thereof, electrical means connected across said center conductor means and said shell means, conductive means secured to said shell means for shielding the openings therein, said electrical means being solderable and removable so that the character of said electrical means may be interchangeably varied.

2. A connection as in claim 1, wherein said electrical means include second coaxial cable means having second outer conductor means secured to said shell means'and also having second center conductor means connected to said first center conductor means at said holding means.

3. A device as in claim 1, wherein said electrical means include a terminating resistance.

4. A connection as in claim 1, wherein said centering means include a conductive tube mounted in said spacer means along the axis of said shell means and surround a portion of said center conductor means.

5. A connection is an claim 1, wherein said tube and said shell means together with said shielding means have respective diameters conforming to the characteristic impedance of said connection to the characteristic impedance of said cable means.

6. A connection as in claim 1, wherein said tubular shell means have axial tubular projections on both ends thereof at least one of which has a diameter equal to the diameter of said outer conductor means on said cable means and projects under the outer conductor means of said cable means, and ferrule means crimped about the outer conductor means of said cable means and said one of said projection means for securing said shell means to said cable means.

7. A connection as in claim 6, wherein said electrical means include second cable means having outer conductor means surrounding the other of said projection means and second ferrule means crimped about said sec- 0nd outer conductor means and said the other one of said projection means for securing said second cable means to said shell means, said second cable means having second center conductor means solder-connected to said first center conductor means.

8. A connection as in claim 3, wherein said conductive means extend beyond one end of said shell means for protecting said electrical means.

9. A cable connector, comprising conductive tubular shell means, cylindrical flange means smaller in diameter than said shell means and extending coaxially therefrom for receiving the outer conductor of a coaxial cable, two axially-separated dielectric spacer means mounted in said shell means, conductive holding means mounted coaxially in said shell means by said spacer means for receiving the center conductor of a coaxial cable, said shell means defining a radial aperture located between said spacer means for exposing said holding means, and conductive means secured to said shell means for shielding said aperture, said aperture being sufficiently large to allow a joining tool to joinsaid conductive holding means to the center conductor of a coaxial cable, said conductive holding means having an end opening for receiving the center conductor.

10. A connector as in claim 9 wherein said holding means include a conductive tube mounted in said spacer means along the axis of said shell means, said tube having a radial hole in alignment with the aperture.

11. A connector as in claim 10 wherein said tube has a second hole in alignment with the aperture so as to enable a solder tool to enter the aperture and to apply solder to the interior of said tube through the holes.

References Cited UNITED STATES PATENTS 2,152,540 3/1939 Scott et al. l7475.2 2,891,223 6/1959 Dolin et al l7475.2 XR 2,970,184 1/1961 Blonder 174-88 DARRELL L. CLAY, Primary Examiner US. Cl. X.R. 17475; 333-22 

